Electrical cavity resonator



Nov. 8, 1949 L. USSELMAN ELECTRICAL CAVITY RESONATOR Filed Nov. 16, 1943 INVENTOR ATTORNEY Patented Nov. 8, 1949 ELECTRICAL CAVITY RESONATOR George L. Usselman, Port J efierson, N. Y., assignor to Radio Corporation of America, a. corporation of Delaware Application November 16, 1943, Serial No. 510,495

3 Claims.

This invention relates generally to high frequenoy electrical resonators and, more particularly, to cavity resonators. The term cavity resonator is herein employed to designate a Referring to Figure l in more detail, there is shown the top or bottom view of a cavity resonator of the pancake type, with one end wall removed. The central axis of this cavity resonator closed electrically conducing surface enclosing a 5 is indicated at I 0. The invention resides prihollow space, and wherein the enclosure contains marily in the use of amultiplicity of curved a periodically repeating electromagnetic field. metallic vanes V1, V2 V3 V6, so arranged Heretofore, in using cavity resonators, particusymmetrically around the central axis II] that larly rectangular shaped cavity resonators, it has they can be simultaneously moved to enclose more been customary to change the length of the cavity or less volume of the resonator, and thus vary in order to vary the frequency. When a certain the frequency of the resonator. The vanes are minimum dimension is reached, however, the each hinged at one end atA by means of hinged fwidth becames the length and a further change bolts which pass through the metallic end walls, in the two moving walls does not change the fre- PI, P2. One end wallis not shown in Figure 1 quency, or the action becomes unstable. in order to show the interior of the cavity resona- Among the objectsof the present invention are: tor while the other end wall is shown. The vanes to provide a cavity resonator having improved VI V6, are keyed rigidly to the bolts and tuning means for controlling the frequency of have bearings in the metallic end walls or plates the resonator and which overcomes the fore- At the end of each bolt A there is rigidly going difficulty; to provide a variable frequency fastened an arm M. The ends of the arms M cavityresonator having tuning means which sifarthest removed from the bolts A engage a ring multaneously changes the efiective dimensions of R by means of o h ped holes or pron S- Gear all walls of the resonator; to provide a cavity teeth are cut on a portion of ring R to enga e resonator equipped with tuning means which a pinion ar he ed es of the vanes changes the volume of the resonator in substan- VI V6 are provided with brushes or contact tially symmetrical manner around its central p gs B to make o d e ec rical Contact with axis. the end walls PI, P2 of the cavity resonator, as According to an embodiment of the inve ti n, shown in more detail in Figure 3. These brushes the cavity resonator is provided with tuning may be of any satisf c or yp whi h Will allow means composed of a plurality of curved vanes. e movement of e vanes and e od elec- These vanes surround the central axi of th trical contact with the plates against which they resonator to form a closed wall and are hinged beer. e end Wells e p r ted by at the ends farthest removed from the central Spacers X and also y the 13 1155 A Which hold axis. The other ends of the vanes are in (3011- the plates P rig d y in place Spacers Xmay stant contact with the sides of the neighboring be m f in i m r l or me al, although vanes in all tuning or operating positions, thus metal Spacers are p ed e ause of their forming a closed symmetrical cavity at all times. greater Strength and the e O mac i ing to A gear arrangement is employed to control the the Correct ns onmovement of all vanes simultaneously in unih v nes V V6 are so curved and ar control manner. ranged that the ends of the vanes farthest re- A more detailed description f the i tio moved from the bolts A are in constant contact follows in conjunction with a drawing, wherein W the S s of th e bo n van s in all Figure 1 is a partial sectional view of a cavity of the operating or tuning positions. These conresonator equipped with tuning vanes in accordtact ends are preferably provided with suitable ance with one embodiment of the invention. This brushes that make good electrical contact against view shows the resonator from one end, with the the sides of the neighboring vanes. In this way end wall removed. the vanes always form a closed symmetrical cavity Figure 2 is a schematic diagram of a pair of at all times. This is made possible by the fact cavity resonators having generally the structure that there are employed six vanes which comprise of Figure 1, arranged in an ultra frequency oscilinverted segments on the circle on which they lation generator circuit; and are hinged. These six vanes are unicontr'olled Figure 3 is a detail of the structure of Figures by the gear G and operate to reduce the cavity 1- and 2 and shows the manner in which the volume to an extremely small space when it is vanes contact the top and bottom walls of the desired that the cavity resonator have minimum resonator. volume and the highest frequency position.

The dot and dash lines in Figure 1 indicate the position of the vanes in the maximum volume and lowest frequency position. The position of the vanes shown in Figure 1 is merely given by way of illustration and shows the vanes arranged in an intermediate frequency positionbetween the lowest and highest frequencies of the tuning range.

In operating the cavity resonator of Figure 1, let us .assume that it is desired to increase the frequency of the resonator. To do this, the volume of the cavity must be decreased. To achieve this, the gear G should be turned clockwise. The movement of the gear G in a clockwise direction will turn the ring R. in a counter-clockwise direction and the latter, in turn, will act on the arms M and hinges A to swing the vanes toward the center of the cavity, thus reducing the volume of the cavity of the resonator, as desired. Because the ends of the vanes farthest removed from the hinges A are always in contact with the sides of the neighboring vanes in all or the operating or tuning positions, there will always be formed a closed symmetrical cavity around the central axis ill of the cavity resonator.

Although only six vanes have been shown in the resonator of Figure 1, it should be understood that the invention is not limited to this number since the vanes may have shapes different from that illustrated and may be composed of a number of vanes diirerent from six.

Figure 2 illustrates, by way of example only, a schematic diagram of an ultra high frequency generator employing a pair of cavity resonators constructed in accordance with the principles of Figure l, in conjunction with a vacuum tube T. The pair of cavity resonators of Figure 2 are designated generally by the numerals 2i) and 2! and comprise a circular plate having a top wall Pi and a bottom wall P3 and a common or intermediate wall P2. through all three flat metallic plates Pl, P2 and P3 rigidly maintain these plates in position. The

common wall P2 is provided with an aperture at its center to accommodate the vacuum tube '1. The grid of the tube is capacitively coupled to the wall P2 by means of a metallic flange 2 which is separated from the wall P2 by mica insulation 3. Similarly, the anode of the tube T is capacitively coupled to the end wall Pi by means of a metallic flange which is separated from the wall Pl by means of a mica spacer 3. The capacities between the anode and plate Pi and between the grid and plate P2 are of extremely low impedance to energy of the operating frequency, thus constituting by-pass condensers. Positive polarizing potential for the anode is supplied over lead 6 which passes through an aperture in the end wall PI to connect with the anode flange. Bias for the grid is supplied over lead I which is connected to the grid flange 2. This lead I is preferably taken out through a hole drilled radially in the plate P2. Although not shown in the drawing, the bias for the grid is obtained from a grid-leak resistor in the conventional manner. The cathode oi the tube T is directly connected to the bottom plate P3. The cathode heater leads H are brought out directly from the plate P25 through an aperture. Each of the cavity resonators 2i] and H are provided with the six vanes of Figure l in substantially the same manner shown in Figure 1. Only two vanes, V1 and V4, are shown for the upper cavity resonator Zil and two vanes V1, V4, are shown for the lower cavity The hinged bolts A passing resonator 2|. The vanes, which are oorrespondingly designated, except for the prime designations, are located in the same straight line one above the other and move simultaneously with each other. In order to change the tuning of the cavity resonator there is shown the gear G controlled by means of a knob N fastened to the shaft thereof. To obtain feedback between the cavity resonators '20 and 21 there are provided a pair of conducting loops 4 and 5 in the interior of the resonators. These conducting loops pass through apertures in the plates PI and P3 and connect with a parallel conductor or Lecher wire circuit W1, W2. This Lecher wire circuit is provided with a short-circuiting bar F which is adjustable or movable over the lengths 0f the parallel conductors W1, W2. For tuning the cavity resonators, it is only necessary to turn knob N which will rotate pinion gear G in engagement with ring R. Movement of ring R will cause simultaneous movement of all the vanes within the two cavity resonators through the action of arms M linked to the ring R at one end and linked to the vanes at the other. Turning the gear G in a clockwise direction will decrease the volume of the two cavity resonators 2i] and 2| and increase the frequency of the oscillator, while movement of the gear G in a counter-clockwise direction will increase the volume of the cavities enclosed by the vanes and decrease the frequency of the oscillator.

In a construction of the resonators of the invention, it is preferred that the end walls and the movable elements forming the side walls be made of copper or some other equally good con ducting material. The cavity resonators may, however, be made of any material and its surfaces coated with copper, silver or gold.

What is claimed is:

1. A cavity resonator having flat stationary end walls, and movable side walls in the form of a plurality of movable vanes symmetrically arranged around and surrounding the central axis of said resonator, one end of each vane being pivoted with respect to an axis which is stationary relative to said end walls while the other end of each vane is adapted to engage an adjacent vane at a point intermediate the ends of the adjacent vane.

2. A cavity resonator having stationary top and bottom walls and movable side walls of high conducting material, said side walls comprising a plurality of metallic vanes arranged symmetrically around the central axis of said resonators and in slidable contact at their top and bottom side edges with said top and bottom walls, respectively, said vanes being hinged at theirouter edges and in adjustable contact with adjacent vanes solely at their inner edges, and rotatable means linked to said vanes for moving said vanes simultaneously to thereby change the effective volume of said resonator, said last means including a circular gear which is larger than the effective area of and coaxially arranged with respect to said cavity resonator and located adjacent the outer edges of said vanes, said vanes being separately linked to said gear at their hinged edges.

3. A cavity resonator comprising stationary top and bottom walls and movable side walls, said side walls being composed of a plurality of vanes, means supporting the outer ends of said vanes between said top and bottom walls and in pivoted relation thereto, and revolvable means linked to said vane supporting means for imparting simul- 6 taneous movement to the other ends of said vanes UNITED STATES PATENTS to the same extent and in the same relative Number Name Date direction 2 044 413 Weyrich June 16 1936 GEORGE USSELMAN- 5 2,261,130 Applegate Nov. 4, 1941 2,367,576 Harvey Jan. 16,1945 REFERENCES CITED 2,404,261 Whinnery July 16, 1946 The following references are of record in the 2,406,370 Hansen Aug. 2'7, 1946 file of this patent: 2,410,109 Schelleng Oct. 29, 1946 

